Optical recorder

ABSTRACT

Non-impact printing or recording apparatus adapted for use with a digital computer. The apparatus is characterized by the employment of an optical character generator and timing system therefor capable of printing information on a moving photoresponsive medium.

United States Patent Chen [451 July 18, 1972 [54] OPTICAL RECORDER [72]Inventor: Philip L. Chen, Penfield, NY.

[73] Assignee: Xerox Corporation, Stamford, Conn.

[22] Filed: Dec. 28, 1970 [21] Appl.No.: 101,671

3,249,028 5/1966 Higonnet et a1 ..95/4.5 R 2,726,940 12/1955 Buhler....95/4.5 R 3,252,392 5/1966 Ward ....95/4.5 R 3,262,379 7/ 1966 Baueret a]. ..95/4.5 R

Primary Examiner-Samuel S. Matthews Assistant Examiner-Robert P. GreinerAttorney-James J. Ralabate, John E. Beck and Benjamin B. Sklar 5.7ABSTRACT Non-impact printing or recording apparatus adapted for use witha digital computer. The apparatus is characterized by the employment ofan optical character generator and timing system therefor capable ofprinting infonnation on a moving photoresponsive medium.

10 Chins, 14 Drawing Figures PATENTED JULI 8 I972 SHEET 1 [1F 8 INVENTORPHILIP L. CHEN msmm m 1 a ma sum 2 [IF 8 PAYENTED Jun 8 m2 7 SHEET 5 UB8M NNNNNNN PATENTEU JUU 8 I972 SHEET 8 OF 8 PATENTED JUL 1 8 I972 SHEET 7OF 8 I PATENTED H l972 $677,148

' SHEET 8 UF 8 ME COLUMN l 2 3 4 T o sTART OFLINE V ONE T CHARAC ER(START OF FIRST QUADRANT). SPACES) OPTICAL I l AXIS l sec. (END OF FIRSTQUADRANT) 9 SEC.

(sTART OF SECOND QUADRANT) b d/ sec. (START OF THIRD IQUADRANT) sec.

(END OF THIRD QUADRANT) SEC.

(START OF FOURTH QUADRANT) 9 sec.

(END OF FOURTH QUADRANT) Z END OF um:

FIG /3 OPTICAL RECORDER BACKGROUND OF THE INVENTION This inventionrelates, in general, to high speed printing and, more particularly, tooptical character printers compatible with digital computer output.

Earlier attempts at computer output printing of the type hereincontemplated led to the development of shadowgraph printing whereinillumination from a flash lamp passes through transparent characters tothereby form a shadow image or images on a recording medium.

Exposure in such a system is determined by the solid angle subtended bythe flash lamp arc at the character mask. Hence, exposure increases asthe arc size is increased or as a given lamp is moved closer to thecharacter mask. Since a finite distance is required to separate aphotosensitive recording medium such as selenium from the charactermask, the light rays from the lamp are constrained in angular deviationto small angles for acceptable character image quality. Consequently,image quality directly opposes exposure in that the lamp arc must beeither made smaller or moved away from the character mask to improveimage quality. Such movement, in turn, necessitates a higher powerinput.

A compromise solution to the foregoing problem results in the employmentof a very small flash lamp, requiring a very small xenon fill pressurewhich varies widely in the manufacturing process, resulting invariations in light output from lamp to lamp. Furthermore, the wall areato electrode volume ratio is small, consequently, lamp blacking causedby electrode sputtering limits the life of the lamp to about flashes at8 millijoules per flash. Still further such lamps are limited to 1: 1printing.

In solving the foregoing problem one may utilize small unconfined,commercially available, arc lamps which have a life greater than 10flashes at 8 millijoules per flash. A simple lamp cover enclosing eachlamp can be provided as a partial diffuse integrating cavity. To carrythe light from the lamp to the recording medium, with shadowgraphing oroptical imaging, an incoherent fiber bundle could be provided. Such anarrangement exhibits a very low efficiency (i. e. about 20 percent)which requires a very high energy input which substantially shortens thelife of the lamp.

characteristically incoherent fiber bundles when illu minated with asmall light source placed in close proximity thereto produces unevenillumination. Moreover, such devices are bulky and complicated. Forexample, for a computer printout format of 132 columns, the printerneeds 132 flash lamps and related circuitry plus 132 fiber bundles allof which have to be packed into a character mask structure.

Accordingly, the general object of the invention is to provide new andimproved printing apparatus.

It is a more particular object of this invention to provide new andimproved printing apparatus wherein computer outputs of 132 charactersper line can be printed on an 11 inch wide copy sheet.

Another object of this invention is to provide a new and improvedoptical system for an optical printer.

Still another object of this invention is to provide a new and improvedcharacter mask for use in an optical printer.

Yet another object of this invention is to provide a new and improvedprinting apparatus utilizing optical imaging on a rotatingphotoconductive drum.

BRIEF DESCRIPTION OF THE INVENTION Briefly, the above-cited objects areaccomplished by the provision of a transparent character drum havingstaggered columns or sets of characters extending about thecircumference thereof. In the preferred embodiment there are 132 suchcolumns divided into groups of four such that each group of four columnsextends around the entire circumference of the character drum. In thismanner there are 33 groups of four columns each.

The groups are spaced apart along the longitudinal axis of the drum adistance at least equal to the distance across one group. This permitsthe projection of properly spaced, enlarged images, onto a rotatingphotoconductive drum.

A strip prism arrangement of equivalent mirror system cooperates with 33commercially available flash lamps and suitable condenser lenses totransmit illumination from the lamps through the character drum imagesin the direction of a strip lens structure serving to form the images ona rotating photoconductive drum. The individual elements of the prismarrangement are disposed relative to one another so as to interceptlight travelling in three different directions and transmit the lighttherefrom in one direction so that in conjunction with suitable timingmeans associated with the character drum, an entire line can be printedfor each revolution of the character drum.

The timing means comprises a plurality of slits on the character drumwhich are so arranged with respect to the characters on the characterdrum that all the characters to be contained in a line on thephotoconductive drum can be registered in that line even though thevarious characters forming the line pass the light from the prisms atdifferent points in time and even though the photoconductive drum iscontinuously rotating.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a schematic viewof printing apparatus representing the invention;

FIG. 2 is a schematic perspective view of an optical character mask andoptical projection system forming a part of the apparatus illustrated inFIG. 1;

FIG. 3 is a block diagram depicting the cycle of operation forgenerating optical characters by means of the mask and projection systemof FIG. 2;

FIG. 4 is an expanded view as viewed from the outside of .the charactermask illustrated in FIG. 2;

FIG. 5 is an expanded view as viewed from the outside of a charactermask utilized for the purpose of providing a better understanding of theinvention;

FIGS. 6 and 7 are schematic perspective views of the character drum ofFIG. 5 illustrating the projection of the characters thereof onto aphotoconductive surface;

FIGS. 8-10 are similar to FIGS. 5-7, but illustrate a timing slitarrangement and its effect on the projection of characters onto thephotoconductive surface;

FIG. 11 is an enlarged schematic perspective view of the optical systemforming a part of the invention;

FIG. 12 is a schematic perspective view illustrating a field markforming a part of the projection system hereof;

FIG. 13 is a time sequential representation of the characters on thecharacter mask at the time of their projection onto the photoconductivesurface as viewed through a stationary field mask; and

FIG. 14 is an enlarged plan view of the field mask and character maskillustrating the simultaneous projection of three consecutive charactersof the character mask.

DETAILED DESCRIPTION OF THE INVENTION GENERAL As shown schematically inFIG. 1, the automatic xerographic recording apparatus comprises axerographic plate 20 including a photoconductive layer orlight-receiving surface on a conductive backing and formed in the shapeof a drum, which is mounted on a shaft journalled in a frame to rotatein the direction indicated by the arrow to cause the drum surfacesequentially to pass a plurality of xerographic processing stations.

For the purpose of the present disclosure, the several xerographicprocessing stations in the path of movement of the drum surface may bedescribed functionally, as follows:

A charging station, at which a uniform electrostatic charge is depositedon the photoconductive layer of the xerographic drum;

An exposure station, at which a light or radiation pattern ofinformation to be recorded is projected onto the drum surface todissipate the drum charge in the exposed areas thereof and thereby formlatent electrostatic images of the information to be recorded;

A developing station, at which xerographic developing material includingtoner particles having electrostatic charges opposite to that of theelectrostatic latent images are cascaded over the drum surface, wherebythe toner particles adhere to the electrostatic latent images to formxerographic powdered images in the configuration of the informationbeing recorded.

A transfer station, at which the xerographic powder images areelectrostatically transferred from the 'drum surface to a transfermaterial or support surface; and,

A drum cleaning and discharge station, at which the drum surface isbrushed to remove residual toner particles remaining thereon after imagetransfer, and at which the drum surface is exposed to a relativelybright light source to effect substantially complete discharge of anyresidual electrostatic charge remaining thereon.

The charging station is preferably located, as indicated by referencecharacter A. As shown, the charging arrangement includes a coronacharging device 21 which includes a corona discharge array of one ormore corona discharge electrodes that extend transversely across thedrum surface and are energized from a high potential source and aresubstantially closed within a shielding member.

Next subsequent thereto in the path of motion of the xerographic drum isan exposure station E. A flash expose optical projection system isprovided to project an image onto the surface of the photoconductivedrum.

The optical projection system comprises a stationary lens and prismstructure generally indicated 23 comprising a plurality of prismsarranged to reflect light, emanating from a plurality of directions, inone direction through a character mask in the shape of a drum 24. Thelamps associated with the prisms and character mask are adapted to beflashed in accordance with output from a digital computer, in such amanner as to enable printing of an entire line for each revolution ofthe character drum.

Adjacent to the exposure station is a developing station C in whichthere is positioned a developer apparatus 30 including a casing orhousing having a lower or sump portion for accumulating developermaterial. A bucket type conveyor is used to carry the developingmaterial to the upper part of the developer housing where it is cascadedover a hopper chute onto the xerographic drum to effect development. Atoner dispenser 35 is used to accurately meter toner to the developingmaterial as toner particles are consumed during the developingoperation.

Positioned next and adjacent to the developing station is the imagetransfer station D which includes a sheet feeding arrangement adapted tofeed sheets of support material, such as paper or the like, successivelyto the xerographic drum in coordination with the presentation of thedeveloped image on the drum surface at the transfer station.

The sheet feeding mechanism includes a sheet feed device 40 adapted bymeans of vacuum feeders to feed the top sheet of a stack of sheets on atray 41, to rollers 42 cooperating with the belts of paper transport 44for advancing the sheet sulficiently to be held by paper transport 44which in turn, conveys the sheet to a sheet registration device 45positioned adjacent to the xerographic drum. The sheet registrationdevice arrests and aligns each individual sheet of material and then intimed relation to the movement of the xerographic drum, advances thesheet material into contact with the xerographic drum in registrationwith a previously formed xerographic powder image on the drum.

The transfer of the xerographic powder image from the drum surface tothe sheets of support material is effected by means of a corona transferdevice 51 that is located at or immediately after the line of contactbetween the support material and the rotating drum. In operation, theelectrostatic field rotating brush 71, and a discharge lamp LMP1 adaptedto flood the xerographic drum with light to cause dissipation of anyresidual electrical charge remaining on the xerographic drum.

For collecting powder particles removed from the xerographic drum by thebrush 7], there is provided a dust hood 73 that is formed to encompassapproximately two-thirds of the brush area. To ensure thorough cleaningof the brush, a flicking bar 74 is secured to the interior of the dusthood adjacent the edge of the outlet duct 75 of the dust hood and ininterfering relation with the ends of the brush bristles whereby dustparticles may be dislodge therefrom.

For removing dust particles from the brush and dust hood, an exhaustduct 76 is arranged to cover the outlet of the dust hood, the exhaustduct being connected at its other end to the wall of a filter box 77attached to the dust hood. A filter bag 78 is secured within the filterbox, with the mouth of the filter bag in communication with exhaustduct. Motor fan unit MOT-6, connected to the filter box, produces a flowof air through the filter box drawing air through the area surroundingthe xerographic drum and the dust hood, the air entraining powderparticles removed from the drum by the brush as the air flows throughthe dust hood. Powder particles are separated from the air as it flowsthrough the filter bag so that only clean air reaches the motor unit.

Suitable drive means are provided to drive the drums and sheet feedmechanism at predetermined speeds relative to each other and to effectoperation of the bucket-type conveyor and toner dispenser mechanism andthe other operating mechanisms.

The character mask or drum 24 form a part of an optical projectionsystem comprising the lens and prism structure 23, to be discussed indetail hereinafter, and a plurality of flash lamps 100.

The flash lamps are flashable in accordance with information derivedfrom a computer, the illumination therefrom being directed by means ofthe lens and prism structure 23 through characters of the character mask24 which characters may be either opaque or transparent. The charactersso formed produce latent electrostatic images of alphanumeric characterson the photoconductive plate 20.

Each of the character space occupied by a character on the xerographicplate is associated with a transparent slit or aperture 102, the slitsbeing disposed about the circumference of the drum. A slit sensor 104disposed adjacent the outer surface of the drum intercepts a light froma light source 106 each time a slit 102 passes between the sensor andthe light source. Pulses generated by the sensor 104 are utilized, aswill be discussed hereinafter, to effect firing of the lamps 100.

The block diagram of FIG. 3 illustrates, in general, the cycle ofoperation for firing of the flash lamps in accordance with the outputfrom a computer 108 which is utilized as a buffer storage devicecontaining sufficient data to print a complete page of 66 lines. A modelDD? 516 computer manufactured by Honeywell Corporation has beensatisfactorily employed to demonstrate the operation of the printer.

Initially only a portion of the data contained in the buffer device 108is written into a memory device 110 which may comprise a pair of F1 40fast access memory cards having a capacity of 16 two-character words at16 bits per word. Such cards are manufactured by Xerox Data Systems.Writing into memory is accomplished by means of a process control shiftregister 112 driven by a 5 MHz clock. The shift register also controlsthe reading of the data into a comparator 114 which may comprisesuitable logic components, for example, AND gates (not shown) forderiving outputs when positive comparisons are made. The other input tothe AND gates may be derived from a counter 116.

The counter 116 is preset to a code representing the first character onthe character drum 24. Accordingly, when the first or initial portion ofdata is read into the comparator 110 it is compared to the coderepresenting the aforementioned first character or in other words thepreset value of the counter. Each successive character on the characterdrum is represented by a code in the counter on incrementing thereof.This incrementing of the counter is accomplished by virtue of the pulsesfrom the slit sensor 104. It can be seen that the code representing thesecond character on the drum will be represented by the preset value ofthe counter plus 1.

When the code in the comparator 114 is the same as the code from thememory 110, a latch 118, which may comprise a flip-flop (not shown) isset. Pulses from the sensor 104 are ANDed with the outputs from thelatches to thereby actuate lamp firing circuits 120.

In accordance with the objects of the present invention, the' charactermask or drum 24, as illustrated in FIG. 4, comprises columns 124 ofcharacters disposed on the periphery thereof in groups of four columns.In the preferred embodiment of the invention 33 such groups of fourcolumns each, are disposed along the longitudinal axis of the drum, eachgroup being spaced from adjacent groups by at least a distance equal tothe width of one group of columns. The circumferential extent of onegroup of columns is such that each column of a group occupies adifferent quadrant of the drum. This produces a staggered arrangement ofthe columns or character sets which permits utilization of one flashlamp for each group of four columns. If the columns were not staggeredbut were disposed in a side by side array, a lamp would be required foreach column. 7

Since the columns 124 are staggered, each flash lamp 100 is fired fourtimes for each revolution of the character drum. Accordingly, during onerevolution, data corresponding to the first column of each group is putinto the comparator 114 and compared against the code in the counter116. Since one fourth of the data in the buffer is handled at one time,this quantity of data may be thought of as one quadrant of data.

For each column of information from the memory 110 that contains an A, acorresponding latch 118 is set. Subsequent thereto, when the slit 102associated with the character space for the A is sensed by the sensor104, the lamp firing circuits 120 corresponding to the latchespreviously set are triggered. Simultaneously, the pulse from the sensor104 increments the counter 116 by one. The code for the letter B is nowin the comparator and is subsequently compared to the first quadrant ofdata from the buffer. Each character of the first column is compared inthe foregoing manner to the first quadrant of data.

At the end of each column 124 adjacent the last character space of thatcolumn there is provided a transparent slit 125 which effects pulsing ofa photodetector 132, the pulse from which conditions the register 112for writing the second quadrant of data from the buffer into memory withsubsequent reading from memory into the comparator. The second quadrantof data is read into the comparator, as before, for each character ofthe second column, each character of the second column being placed oneat a time into the comparator as above. The sequence of operation forthe third and fourth quadrants of data from the buffer is the same asdescribed above.

As can be seen from FIG. 4, the slits 102 do not occupy the samerelative position with respect to their associated character spaces. Inother words the slit associated with the first letter of any firstcolumn is disposed adjacent the trailing edge of the first characterspace assuming that the character mask of FIG. 4 is moving upwardly pasta flash exposure station. The slit associated with the last character ofthe group is adjacent the leading edge of that character space.

The purpose of the specific arrangement of the slits 102 will be betterunderstood by first considering the operation of a character mask onwhich the slits are spaced the same, relative to each character space i.e., adjacent the trailing edge of the wherein there is disclosed anexpanded view as viewed from the outside (FIG. 5) of a character mask ordrum having a plurality of columns 142 of characters disposed thereon ina side by side relationship. The character drum is adapted for rotationin the counterclockwise direction while a photosensitive insulatingplate 144 optically aligned therewith is adapted for rotation in theclockwise direction.

Each column 142 of characters, herein illustrated as the capital lettersof the alphabet, represents a character set which extends over theentire circumference of the character drum. In the present embodiment itis desired to print a complete line of characters on the photoconductiveplate 144 which line comprises one character from each column of thecharacter drum. Accordingly, flash lamps, not shown, associated, onewith each column, will flash once for each revolution of the characterdrum. Meanwhile, the photoconductive plate rotates the equivalent of onecharacter space. A column of timing slits, one for each character of acolumn, generally indicated by reference character 146, is sensed tothereby cooperate with an output from a computer to cause flashing ofthe lamps in accordance with the characters to be recorded. In thisparticular embodiment each timing slit occupies the same positionrelative to the character space associated with a particulate character,as all other slits. In other words, each timing slit is in line with thetrailing edge of the character space occupied by the characterassociated therewith.

As shown in FIG. 5, the character A from the first column from the left,is projected onto the photoconductive plate in the position shown, whichposition lies below a stationary reference line 148 used herein forillustration purposes only. Assuming that the Z of the fourth column isto be projected onto the plate, it will be seen that because thephotoconductive plate has moved clockwise a full line or character spacethe Z is projected onto the drum, not on the same line space as the Abut one line space below. This is due to the fact that with such atiming slit arrangement all characters are projected below the referenceline and by the time the Z moves through the optical axis the line spaceon the drum containing the A has moved above the reference line.

In order to obviate this problem a plurality of differently spacedtiming slits 150, one for each character set is provided adjacent theright edge of a character drum 152. (See FIGS. 8-10). These slits orindicia may be apertures in the character drum or transparent windows inan opaque mask. Either of the foregoing may be employed, the essentialrequirement being the capability of passing light from the light source106 to the light sensor 104 which may be a photodiode. The sensor andlight source are in line with the optical axis extending between the twodrums.

The slits or windows, as shown in FIG. 8 are arranged relative tocolumns 154 of character drum 152 such that the one associated with theA is substantially in line with the trailing edge of the character spaceoccupied by the A and the one associated with the character spaceoccupied by the Z is substantially in line with the leading edge of thecharacter space occupied by the Z. The slits or windows intermediate theones associated with the A and Z are incrementally progressed such thatthe one associated with the M is substantially in line with the middleof the character space occupied thereby. It can be seen from FIG. 8 thatwhen the slit associated with the A (first column from left) passes thelight sensor 104, the A is projected onto a plate 156 in an area thatlies below an reference line 158. From FIG. 10, it can be seen that whenthe slit associated with the Z (fourth column from left) passes thelight sensor, the Z on the drum is in a position so as to be projectedonto the plate in a position above the reference line, which positiondue to the clockwise rotation of the plate is in line with the positionof the A.

In the preferred embodiment of the character mask, columns 124, as shownin FIG. 4, are placed on a character drum 24 in groups of four, the drumbeing sufficiently long (i. e. 9.9 inches) to place thirty-three suchgroups thereon with a space between groups greater than the distanceacross the columns in any one group. As shown the columns of each groupare staggered such that the columns in one group, beginning with thefirst character of the first column or set from the left, and endingwith the last character of the fourth column or set, extendsubstantially the circumference of the drum. As in the case of theembodiment of FIGS. -7, it is intended that a line comprising acharacter from each column or set be printed for each revolution of thedrum.

Since the columns of one group, in the embodiment shown, occupy only onefourth of the circumferential extent or one quadrant of the drum, fourcharacters from each group must be projected onto the same line of aphotoconductor plate for each revolution of the character drum 24.Expressed another way, a character from each column in a group must beprojected for every one-quarter revolution of the character drum. Duringthis quarter revolution the line space on the photoconductive platemoves one fourth its total distance. This means that for the charactersfor any two adjacent columns to be projected onto the same line space ofthe plate, the timing slits 102 associated with those two charactersshould be approximately one fourth the total distance between the firstand last timing slits of one group. To this end the character drum 24is, as shown in FIG. 4, the first one of timing slits 102 is in linewith the trailing edge of the character space associated with the A andthe last timing slit of fourth column of the first group is in line withthe leading edge of the character space associated with the last Z inthat group. It will be seen upon further examination that the tintingslit associated with the character space associated with the z of secondcolumn of the same group occupies a space in line with the middle of theZ.

While the number of columns in each group is illustrated as being four,this need not be the case. Any number of convenient columns may beemployed depending on the particular application and the end resultdesired.

By referring to FIGS. 1 and 4 and bearing in mind the discussionrelative to FIGS. 5-7, it can be seen that for each group of columns, anA, by way of example, can be projected onto and along the same line ofthe plate 20 for each column position of the character drum. Projectionof characters commences when the timing slit associated with the first Aof the first column is sensed by the light sensor. At this time thefirst A is projected onto the plate which then rotates clockwise onefourth of a line space while the character drum rotates approximately aquarter of a revolution. Now the timing slit for the second A is sensedby the light sensor. It will be apparent that the differential spacingof these two timing slits relative to their respective A's causes thesecond A to be projected onto the photoconductive plate a distance onefourth of a line space higher than the preceding A thereby placing thesecond A on exactly the same line on the plate as the first A. Withrespect to the third A, it will be seen that its timing slit will havethe effect of causing the third A to be projected one half of a linespace higher on the plate thereby placing it on the same line with thefirst two characters. Simultaneously, the projection of other first,second and third As of the other groups has taken place along the sameline of the plate.

The slit sensor 104 is disposed, for sake of convenience 90 from theoptical axis. However, it may occupy any location relative to the mask.

The lens and prism structure 23, as best shown in FIGS. 1 and 11,comprises a prism structure 160 which may be fabricated as a singlepiece or may be assembled from individual pn'sm elements 162 and blocks163. A plurality of strip condensers 164 comprising individual condenserelements 166 cooperate with condenser elements 167 molded on the stripprism to collect the illumination from the lamps 100 for transmission tothe prism elements 162.

The lamps 100 of which there are thirty-three in the preferredembodiment are arranged in three rows to form an arc of approximately270 about the top, bottom and rear sides of the strip prism structure160. The rows of lamps are offset to each other, the top row beingoffset to the right side of the back row, as viewed from the left inFIG. 11, while the bottom row is offset to the left side of the top row.The amount of offsetting in each of the foregoing cases is equal to fourcolumn widths at the photoreceptor 20. The collected light from eachlamp in the top and bottom rows is reflected by the strip prismstructure in the forward direction toward the character mask 24. Whilethe orientation of the top and bottom lamps are illustrated as beingapproximately 90 from the back row any practical angle orientation isconsidered within the scope of this invention.

The light output from the back row of the lamps travels straight throughthe blocks 163 which are disposed intermediate a pair of prism elements162.

The illuminated characters are magnified approximately three times andare projected onto the photoconductive drum 20 by means of a strip lens170. One element (i. e. one individual lens) of the strip lens covers orimages" four characters on the drum. As shown, these reduced sizecharacter columns are grouped on the character drum leaving theaforementioned spaces between groups, hence, the character groups arereadily baffled by means of a bafile structure 172 to thereby preventoptical cross-talk between strip lens elements.

A stationary field mask 180 (FIG. 12) interposed between the strip lensand the photoconductive drum or plate 20 permits center-to-center(measured circumferentially) compression of characters on a charactermask 181 resulting in optimization of the required rotational velocityof the character mask and the required optical magnification from thecharacter mask to the photoconductive drum 20. The field mask comprisesan opaque portion 182 and a plurality of clear portions or windows 185,one such clear portion for each character. Each group of four windowsforms a stepped pattern which in combination with the slits 102 serves apurpose which will be discussed hereinafter.

FIG. [3 illustrate the time sequence of the characters A and Z on theoutside of the character mask 181 at the time of their projection. Byway of example, these two characters are intended to represent the firstand last characters of each column or character set. One group of fourcolumns is taken as representative of the entire character mask. Itfollows from a study of FIG. 13 that the stationary field maskillustrated in FIGS. 12 and 14 in no way inhibits the projection of anyof the characters shown in FIG. 13. It is noted that the vertical heightof the transparent portions 184 is 25 percent larger than one characterspace.

FIG. 14 illustrates that if the characters within a character set orcolumn are separated by one quarter of a character space, and the maskis employed, one and only one character from a particular column isprojected at a given time. The stepped portions are repetitive for eachgroup of drum diameter and angular velocity to remain the same whileincreasing the size of the characters on the character drum and hencereduce the required optical magnification of the characters. Also, theresulting system has advantageous tolerancing effects as will beappreciated by those skilled in the art.

What is claimed is: 1. Apparatus for recording alphanumeric characters,said apparatus comprising:

an endless member having staggered columns of transparent charactersextending about the circumference thereof, said columns being disposedin groups of at least two columns which groups extend transversely ofsaid endless member and are spaced apart at least the distance across asingle group of columns,

first optical means for projecting in one direction, collimated lightemanating from a plurality of directions, said optical means beingdisposed within said endless member,

a plurality of flash lamps, one for each group of columns,

said flash lamps being disposed in rows of equally spaced lamps whichrows are offset one from the other and disposed in an arc extendingabout said first optical means;

second optical means for focusing light passing through said endlessmember at a focal point;

light responsive recording structure positioned at said focal point forreceiving focused images of alphanumeric characters;

means for rotating said endless member at a uniform speed,

and

means for selectively flashing lamps in accordance with information tobe recorded.

2. Apparatus according to claim 1, including means for moving said lightresponsive structure in synchronization with said endless member, andwherein said means for selectively flashing said lamps comprises meansfor effecting flashing of said lamps in a predetermined timerelationship to said lamps whereby a line of input characters in focusedon said light sensitive member in a substantially straight line.

3. Apparatus according to claim 1, wherein said light responsiverecording medium comprises an electrostatic charge-retentive surface andsaid apparatus further comprises:

means for placing a uniform charge on said surface which is dissipatedin accordance with images focused thereon to thereby form anelectrostatic image, and

means for developing said latent image in order to render visible.

4. Apparatus according to claim 3, further including means fortransferring an image to a copy sheet.

5. Apparatus according to claim 1, wherein:

said means for transmitting collimated light comprises a row of prismsin parallel blocks having light receiving and light emanating surfaces,said light emanating surfaces being disposed in one row while said lightreceiving surfaces of said prism are arranged in two rows and the lightreceiving surface of said parallel blocks are disposed and a third row,all rows being spaced a multiple 90 from said light emitting surfaces.

6. Projection imaging apparatus for use in an alphanumeric recordingapparatus employing a light responsive recording medium, said structurecomprising:

a character mask having light transmitting characters formed thereon;

means for moving said character mask at a substantially uniform speed;

means for intercepting collimated light emanating form a plurality ofdirections and transmitting said light through said character mask alonga fixed line;

a plurality of rows of selectively flashable lamps disposed in an areextending partially around said light intercepting means, and

means for flashing said lamps in accordance with information to berecorded.

7. Structure according to claim 6, wherein said means for tramsmittinglight comprises a row of prisms and parallel blocks having lightreceiving and light emitting surfaces, said light emitting surfacesbeing disposed in one row while said light receiving surfaces aredisposed in a plurality of rows which are spaced at least from saidlight emitting row.

8. Structure as specified in claim 7, including means for focusingimages onto a light responsive recording medium.

9. Structure as specified in claim 8, wherein said character maskcomprises groups of circumferentially staggered columns of charactersand wherein the number of flashable lamps is equal to the number ofgroups of columns.

10. Apparatus for recording alphanumeric characters, said apparatuscomprising:

an endless member having staggered columns of transparent charactersextending about the circumference thereof, said columns being disposedin groups of at least two columns which groups extend transversely ofsaid endless member;

means for selectively producing illumination in accordance withinformation to be recorded; means for pro ecting illumination throughsaid endless member and focusing character images on a light responsivemember;

means for rotating said endless member at a uniform speed;

a light responsive member and means for moving said member at a speedsuch that it moves a distance equal to He X s during l/c of revolutionof said endless member, where c is equal to the number of columns in onegroup and s is equal to the height of a character on said lightresponsive member; and

means for energizing said illumination means in accordance with therelative positions of said endless member and said light responsivemember whereby the character images formed during one revolution of saidendless member are formed along the same line on said light responsivemember.

* IIK

1. Apparatus for recording alphanumeric characters, said apparatuscomprising: an endless member having staggered columns of transparentcharacters extending about the circumference thereof, said columns beingdisposed in groups of at least two columns which groups extendtransversely of said endless member and are spaced apart at least thedistance across a single group of columns, first optical means forprojecting in one direction, collimated light emanating from a pluralityof directions, said optical means being disposed within said endlessmember, a plurality of flash lamps, one for each group of columns, saidflash lamps being disposed in rows of equally spaced lamps which rowsare offset one from the other and disposed in an arc extending aboutsaid first optical means; second optical means for focusing lightpassing through said endless member at a focal point; light responsiverecording structure positioned at said focal point for receiving focusedimages of alphanumeric characters; means for rotating said endlessmember at a uniform speed, and means for selectively flashing lamps inaccordance with information to be recorded.
 2. Apparatus according toclaim 1, including means for moving said light responsive structure insynchronization with said endless member, and wherein said means forselectively flashing said lamps comprises means for effecting flashingof said lamps in a predetermined time relationship to said lamps wherebya line of input characters in focused on said light sensitive member ina substantially straight line.
 3. Apparatus according to claim 1,wherein said light responsive recording medium comprises anelectrostatic charge-retentive surface and said apparatus furthercomprises: means for placing a uniform charge on said surface which isdissipated in accordance with images focused thereon to thereby form anelectrostatic image, and means for developing said latent image in orderto render visible.
 4. Apparatus according to claim 3, further includingmeans for transferring an image to a copy sheet.
 5. Apparatus accordingto claim 1, wherein: said means for transmitting collimated lightcomprises a row of prisms in parallel blocks having light receiving andlight emanating surfaces, said light emanating surfaces being disposedin one row while said light receiving surfaces of said prism arearranged in two rows and the light receiving surface of said parallelblocks are disposed and a third row, all rows being spaced a multiple90* from said light emitting surfaces.
 6. Projection imaging apparatusfor use in an alphanumeric recording apparatus employing a lightresponsive recording medium, said structure comprising: a character maskhaving light transmitting characters formed thereon; means for movingsaid character mask at a substantially uniform speed; means forintercepting collimated light emanaTing form a plurality of directionsand transmitting said light through said character mask along a fixedline; a plurality of rows of selectively flashable lamps disposed in anarc extending partially around said light intercepting means, and meansfor flashing said lamps in accordance with information to be recorded.7. Structure according to claim 6, wherein said means for tramsmittinglight comprises a row of prisms and parallel blocks having lightreceiving and light emitting surfaces, said light emitting surfacesbeing disposed in one row while said light receiving surfaces aredisposed in a plurality of rows which are spaced at least 90* from saidlight emitting row.
 8. Structure as specified in claim 7, includingmeans for focusing images onto a light responsive recording medium. 9.Structure as specified in claim 8, wherein said character mask comprisesgroups of circumferentially staggered columns of characters and whereinthe number of flashable lamps is equal to the number of groups ofcolumns.
 10. Apparatus for recording alphanumeric characters, saidapparatus comprising: an endless member having staggered columns oftransparent characters extending about the circumference thereof, saidcolumns being disposed in groups of at least two columns which groupsextend transversely of said endless member; means for selectivelyproducing illumination in accordance with information to be recorded;means for projecting illumination through said endless member andfocusing character images on a light responsive member; means forrotating said endless member at a uniform speed; a light responsivemember and means for moving said member at a speed such that it moves adistance equal to 1/c X s during 1/c of revolution of said endlessmember, where c is equal to the number of columns in one group and s isequal to the height of a character on said light responsive member; andmeans for energizing said illumination means in accordance with therelative positions of said endless member and said light responsivemember whereby the character images formed during one revolution of saidendless member are formed along the same line on said light responsivemember.